Monolithic III-nitride power converter

ABSTRACT

A power arrangement that includes a monolithically integrated III-nitride power stage having III-nitride power switches and III-nitride driver switches.

RELATED APPLICATION

This application is based on and claims priority to the of U.S.Provisional Application Ser. No. 60/874,411, filed on Dec. 11, 2006,entitled MONOLITHICALLY INTEGRATED GaN POWER CONVERTER, to which a claimof priority is hereby made and the disclosure of which is incorporatedby reference.

DEFINITION

III-nitride device, including III-nitride power device, as called forherein refers to a semiconductor device that includes a III-nitrideheterojunction having a conductive channel commonly referred to as atwo-dimensional electron gas. The III-nitride heterojunction wouldinclude two semiconductor bodies each being formed of a semiconductoralloy from the InAlGaN system.

FIELD OF THE INVENTION

This invention relates to semiconductor drivers and processes for theirmanufacture and more specifically relates to a novel integrated circuitemploying plural III-nitride power devices and drivers therefor.

BACKGROUND OF THE INVENTION

Integrated circuits (ICs) are well known in which plural silicon devicesare formed in a common chip or die. It is difficult to integrate certainkinds of circuits, for example, a buck converter circuit, which employsa power level synchronous MOSFET, a power level control MOSFET and thedrivers therefor, especially in silicon because of device sizes andinterconnections and the need for integrating high voltage and lowvoltage devices and their drivers in a single silicon die. Because oflayout limitations, the connections between power devices and theirpredrivers would be relatively long and non-linear, introducingundesired parasitics.

It would however be very desirable to provide an integrated circuitcontaining the power semiconductors, their drivers and, in some cases,passive circuit components as well, particularly for ac to dc or dc todc converters, which will occupy a small area on a board and have lowcost. It would also be desirable to improve the performance of suchdevices by reducing the parasitic impedances particularly parasiticinductance caused by device layout and interconnections.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention, the power stage isformed in a III-nitride-based semiconductor body, and integrated (forexample, directly attached to the load or mounted as close as possibleto the load) preferably with the load such that the distance between theload and the power stage is minimized. For example, the power stage mayinclude III-nitride based power switches and III-nitride basedpredrivers for driving the power switches which are together mounteddirectly on the load or disposed as close as possible to the load.

The closeness of the III-nitride-based power stage and the load reducesparasitic inductances due to long leads and wires (present in the priorart) and thus improves the overall performance of the circuit. In onevariation, the III-nitride based power stage may use bumps (such ascopper bumps) to be flip chip mounted to reduce or eliminate wirebonds,and thus further reduce parasitic resistance and inductance. Forexample, the power stage may be flip chip mounted on pads provided onthe load or pads on a circuit board which is mounted on the load.

According to another aspect of the present invention, the load may bemodified to include the proper circuitry to operate the power stage.Thus, the load may operate the power stage eliminating the need for PWMdrivers or the like circuits. That is, for example, a load such as aprocessor may include a PWM driver for controlling the power stagedirectly, instead of sending load requirements to a PWM stage.

In another variation, while the power stage may be physically integratedwith the load, the power stage may be driven from an external PWM driveror the like driver.

An implementation according to the present invention is advantageous forthe following reasons. While vertical conduction PN junction typedevices (e.g. silicon devices) can satisfy the power requirements of aload efficiently, vertical conduction devices are difficult to integratewith a load such as a processor. Lateral PN junction type power devicescan integrate well but cannot satisfy the power requirements of someloads such as processors efficiently (that is the current density oflateral devices are limited). Moreover, conventional devices generate arelatively large amount of heat during operation which would add to thethermal load of the load, an undesirable result.

A III-nitride based power device can run at higher temperatures, islateral and thus can integrate well with a processor, and can readilysatisfy the power requirements of a processor. Moreover, III-nitridebased devices occupy less area per power capability, and, therefore, itis possible to have a III-nitride based device mounted directly on orvery close to a load such as a processor (e.g. on the same substrate asthat used for the processor) with relative ease. Moreover, III-nitridebased power devices can be operated at very high frequencies. As aresult, the passives used in the power stage (e.g. inductor andcapacitors in the output stage) can be reduced in size, which allows forthe integration of the passives along with the power stage and the load.Moreover, DI-nitride based devices have low charge. For all thesereasons, the integration of a III-nitride based power stage with aconventional processor provides significant advantages not found in theprior art.

In accordance with an aspect of the present invention, a lateral IC isformed in a substrate to define a power stage that includes pluralIII-nitride power switching devices and their predrivers and, if,desired, passive circuit components such as gate driver capacitors, on asingle III-nitride heterojunction type structure with parallel spacedand elongated source, gate and drain lines which are interconnected onthe device surface by short, straight conductors where needed. The useof a lateral III-nitride device permits the efficient layout of thepower III-nitride switches and of their driver switches which areseparated by a simple insulation well or the like.

The end structure is monolithically integrated to form any desiredcircuit, such as d-c to d-c converters for use with mobile or otherelectronic applications, particularly, a buck converter for receiving aninput battery voltage and producing a highly regulated, reduced outputvoltage as a power supply to other circuits.

In one embodiment of the invention, a buck converter is formed, having acontrol switch and a synchronous switch which are interconnected suchthat the node between them is connected to an output inductor andcapacitor as usual, while their drivers or predrivers, which provide thegate control signals for the control switch and synchronous switch areformed on extensions, in single respective chips, of the same source,gate and drain regions used for the power device. The level shiftcircuit for the predrivers may also be integrated into the monolithicchip. This then permits a simplified layout for the device, whichdrastically reduces parasitics between the predrivers and powerswitches.

A device according to the present invention has reduced cost and usessmall areas of a circuit board. The integration of the control switchand synchronous switch and their drivers lead to reduced mounting andhandling costs as compared to the costs of mounting and handling thevery small parts when formed as discretes.

Further, the performance of the device is improved, using suitableconnections between the control switch and synchronous switch and theirdrivers, virtually eliminating parasitic inductance.

As to advantages of the predrivers, the cost is very small andperformance is improved, with the devices being fast, low Q and low Rfor low loss. Further, there is a great reduction in parasiticimpedances between the predrivers and the respective power switches.

Substantial benefits are also obtained during fabrication of thepredrivers with the power switches in that the predriver characteristicswill be well matched, being subjected to the same oven temperatures, anddeadtime is well optimized. Further, the trimming of the devices takesplace at the same oven temperature.

The integrated chip may be conventionally packaged and mountable to aheat sink or the like. The microprocessor chip for driving the driversmay be in the same package or closely spaced therefrom.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a power management arrangement according to the priorart.

FIG. 2 illustrates a power management arrangement according to thepresent invention.

FIG. 3 illustrates a circuit diagram for a power management arrangementaccording to one embodiment of the present invention.

FIG. 4 illustrates schematically a top plan view of an integrated111-nitride semiconductor device that includes a power stage and adriver stage according to the present invention.

FIG. 5A is a cross-section taken across section line 5A-5A in FIG. 4viewed in the direction of the arrows.

FIG. 5B is a cross-sectional view taken along line 5B-5B in FIG. 4viewed in the direction of the arrows.

FIG. 6 illustrates a conventional arrangement involving a power stageand a processor.

FIGS. 7A-7C illustrate an arrangement according to the present inventionresulting in reduced parasitics, e.g. parasitic inductances.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a power management arrangement according to theprior art includes a power stage 10, a driver stage 12 operativelycoupled to power stage 10 to control the operation of power stage 10, apulse width modulation (PWM) stage 14 operatively coupled to driverstage 12 to control the operation thereof, and a load stage 16operatively coupled to power stage 10 to receive power from the same.

In prior art arrangements, to maintain the proper supply of power toload stage 16, PWM stage 14 uses a predetermined criteria in order tooperate driver stage 12. For example, a predetermined voltage level atthe output of power stage 10 is used to determine whether driver stage12 should operate power stage 10 to supply more power to load stage 16.In many designs, the predetermined value used for the operation of PWM14 may not necessarily correspond to the instantaneous and transientrequirements of load stage 16 which may surpass the predetermined valueset forth for the design. For example, load stage 16 may be a processorwhich requires a transitory requirement for more power that may surpassthe predetermined value of the design. As a result, the operation of theprocessor may be limited by the predetermined value that limits theoperation of PWM 14.

Moreover, in conventional designs, PWM stage 14 is physically outside ofload stage 16 and needs to be coupled to the same using, for example,wiring or the like. As a result, there may be parasitics (e.g.,parasitic inductances) which can limit the response time to a transitorypower requirement by the load as may be reflected by the variation inthe predetermined values, e.g., a transitory deficit of power reflectedby a sudden loss of voltage at the output of power stage 10.

Referring to FIG. 2, according to one aspect of the present invention,PWM stage 14 and load stage 14 are integrated in order to reduce theparasitics, such as parasitic inductances, due to wiring or otherpackaging elements, whereby the speed of operation of the powermanagement arrangement is improved.

According to another aspect of the present invention, PWM stage 14 isnot only enabled to respond to predetermined values at, for example, theoutput of power stage 10, but is enabled to respond to transitoryrequests from load stage 16 for more or less power. For example, loadstage 16 may instruct PWM stage 14 to discontinue sending signals todriver stage 12 despite low voltage at the output of power stage 10 toavoid overheating. Or, conversely, load stage 16 may instruct PWM stage14 to send signals to driver stage 12 to operate despite having avoltage at the output of power stage 10 that satisfies a predeterminedvoltage value. For example, if load stage 16 is a processor, it may sendsignals to PWM stage 14 to send signals to driver stage 12 despitehaving a high enough voltage at the output of power stage 10 in order toensure ample power supply for an anticipated transitory “processingjob.” Thus, the speed of the load may be increased.

Referring now to FIG. 3, a power management arrangement according to anembodiment of the present invention includes power stage 10 thatincludes power switches for the control of the supply of power to loadstage 16. According to one aspect of the present invention, power stage10 includes two III-nitride switches 18, 20 coupled in a half-bridgeconfiguration and each preferably selected to operate in a DC-DC buckconverter. Thus, III-nitride switch 18, which is series connectedbetween the high side V+ and output node V_(S) of the half-bridge, isthe control switch, while III-nitride switch 20, which is seriesconnected between output node V_(S) and ground G, is the synchronousswitch.

Driver stage 12 includes a high side driver, which is coupled to senddrive signals to the gate of switch 18, and low side driver, which iscoupled to send drive signals to the gate of switch 20. High side driverincludes a pair of high side driver switches 22, 22′ coupled in ahalf-bridge configuration the output of which is coupled to send drivesignals to the gate of switch 18, and low side driver includes a pair oflow side driver switches 24, 24′ coupled in a half-bridge configurationthe output of which is coupled to send drive signals to the gate ofswitch 20. Note that switch 22′ is the low side switch in the high sidedriver half-bridge while switch 24′ is the low side switch in the lowside driver half-bridge. The high side driver is preferablylevel-shifted using a level shifter 26. Thus, according to one preferredembodiment, a boot-strap capacitor 28 may be provided to provide thegate charge necessary for switch 18. As is known from conventionaldesigns, a boot-strap diode 30 charges boot-strap capacitor 28 whenswitch 18 is off and V_(S) swings to ground.

Each of the switches 18, 20, 22, 22′, 24, 24′ includes a drain, a sourceand a gate electrode. For better understanding of the Figures herein,Table I provides numeral identification for the drain, the source, andthe gate of each switch.

TABLE I SWITCH SOURCE DRAIN GATE 18 18S 18D 18G 20 20S 20D 20G 22 22S22D 22G 22′ 22′S 22′D 22′G 24 24S 24D 24G 24′ 24′S 24′D 24′G

Note that according to an aspect of the present invention, load stage 16includes PWM stage 14, which is schematically shown, coupled to driverstage 12 to send control signals to the same.

According to another aspect of the present invention, high side driverswitches 22 and 22′, and low side driver switches 24, 24′ are alsoIII-nitride switches. While switches 18, 20, 22, 22′, 24, 24′ can beenhancement mode devices or depletion mode devices, in one preferredembodiment, switches 18, 20 of power stage 10 are depletion modedevices, while switches 22, 22′ and 24, 24′ are enhancement modedevices. Alternatively, switches 22, 22′, 24, 24′ may be depletion modedevices as well.

It should be noted that while the arrangement according to the presentinvention is illustrated with a buck converter type circuit, it is to beunderstood that an arrangement according to the present invention can beadapted for any desired type of buck/boost dc to dc or ac to dcconverter type circuit.

It should be further noted that V_(S) in a typical application may becoupled to an output circuit that includes an output inductor 35 seriesconnected with V_(S) and an output capacitor 37 that is connectedbetween the inductor and ground as is conventionally known. Thus, in atypical application the output power is supplied to load stage 16 fromthe connection point between output inductor 35 and output capacitor 37.

Conventionally, the high side driver and the low side driver arediscretely packaged and are separately mounted and connected to theirrespective power switches over long connection paths.

In accordance with the present invention, the high and low side driversand the power switches 18 and 20 are integrated into a common monolithicsemiconductor die. If desired, level shift circuit 26 and passives suchas bootstrap capacitor 28 and bootstrap diode 30 may also be integratedinto the common die. FIGS. 4, 5A, and 5B show one embodiment of amonolithic semiconductor die according to the present invention.

In FIGS. 4 and 5A, the same numerals identify the same circuitcomponents of FIG. 3. The basic chip includes, as shown in FIG. 4, of asubstrate 40 which is preferably silicon. A conventional transitionlayer 41 (e.g., AlN) is disposed on silicon substrate 40 and receivesthereon a gallium nitride (GaN) layer 42. An AlGaN layer 43 is formedatop layer 42, to define a heterojunction having a carrier rich regionconventionally referred to as two-dimensional electron gas (2-DEG) 44.The die may be constructed by other techniques with other layers, todefine another type of III-nitride device.

In accordance with one aspect of the present invention, and as bestshown in FIG. 4 and FIG. 5B, an insulation or other barrier 50 is formedin the die and extends to at least the depth of GaN layer 42 to define acontrol device “well” to the left of (or on one side of) barrier 50 anda power device surface to the right of barrier 50. Specifically, atrench may be formed in AlGaN layer 43 and filled with a dielectric toelectrically isolate the control device well by interrupting the 2-DEG.Preferably, the trench may extend all the way to GaN layer 42. Aplurality of spaced parallel electrodes are formed across the surface ofthe chip as shown in FIG. 4 and may be interrupted by the barrier 50.Further, note that, switches 18, 20, and switches 22, 22′, 24, 24′ maybe isolated from one another using the same concept. Specifically, atrench that preferably extends through AlGaN layer 43 and is filled witha dielectric 50 may be provided between the switches as illustrated inorder to interrupt the 2-DEG and thus render the switches electricallyisolated.

Short wire bonds 39 are then employed (as illustrated by FIG. 4) to formthe desired circuit of FIG. 3. Alternatively, conductive vias and bumpcontacts for flip chip mounting can be employed.

It is also possible to integrate bootstrap capacitor 28 in the commondie as best shown in FIG. 5A. Thus, conductive layers 60, 61 (on thebottom of the Si substrate); dielectric layers 62, 63 and bottomconductive layers 64, 65 are employed such that layers 60, 62, 64 definebootstrap capacitor 28.

Bootstrap capacitor 28 can also be integrated on the top of the commondie of FIG. 4 or on the outer package of the device.

The various interconnections in FIGS. 4 and 5A may be formed, at leastpartially by vias through the body of the common die.

The structure of FIGS. 4 and 5A defines a power block according to thepresent invention that includes a driver stage and a power stage. Amicroprocessor 70, serving, for example, as the load stage 16, isconnected to suitably control a PWM stage or the like to operate thegates of driver switches 22, 22′, 24, 24′. Power block may be mounted onthe processor chip/module as close as possible to the chip or alongsidethe chip. In this manner, the advantages described above are realized.

One advantage of a monolithically formed power III-nitride switches 18,20, and driver switches 22, 22′, 24, 24′ is the ease of the fabricationthereof. Specifically, because heterojunction III-nitride powersemiconductor devices take advantage of conduction through a 2-DEG, asingle III-nitride heterojunction may be used as the basis for theactive region of all switches 18, 20, 22, 22′, 24, 24′. The isolation ofthe switches can also be relatively simple. Moreover, the powercapability, switching speed, and breakdown rating of each switch can besimply designed by using the relationship between the drain, the source,and the gate electrodes of the device. Thus, for example, switchesrequiring more current conduction capability can have more active cells(e.g. synchronous switch 20), while switches requiring less currentcarrying capability (e.g. driver switches 22, 22′, 24, 24′) can havefewer active cells. Since the number of active cells is relatively easyto design in, integration of III-nitride switches to obtain a monolithicdevice according to the present invention is advantageouslyuncomplicated.

Referring now to FIG. 6, in a prior art power arrangement the pathbetween power stage 100 and load 110, which can be, for example, aprocessor such as a CPU of a personal computer, includes a plurality ofloops that introduce parasitics which reduce the speed of thearrangement as well as its efficiency. The arrangement may include loops130, 140, 150, each including a parasitic resistance and a parasiticinductance. the arrangement may further include PCB parasitics 170 dueto packaging; e.g. wirebonding, circuit board traces, solder or thelike. Thus, for example, at a switching frequency of about 300 Khz, theoutput inductance loop 120, which may be an output inductor, can reducethe di/dt to less than 350 A/μs, output capacitor loop 130, which may bean electrolytic capacitor, can reduce the di/dt to less than 100 Aμs,ceramic bulk capacitors loop 140 can reduce di/dt to less than 400 A/μs,and ceramic caps loop 150 underneath the socket can reduce the di/dt to1200 A/μs. The arrangement may further include a parasitic loop 160 dueto the connectors of the load (e.g. CPU sockets or the like) which mayfurther introduce parasitics into the arrangement.

Referring now to FIGS. 7A-7C, a power stage according to the presentinvention can increase the switching speed to about 75 Mhz (FIG. 7A),which can in turn reduce the inductance of output inductance loop 120,whereby di/dt can be increased to about 1500 A/μs, or the switchingspeed can be increased to about 20 Mhz (FIG. 7B) to reduce theinductance of output inductance loop, thereby increasing di/dt to 6000A/μs. Referring specifically to FIG. 7C, further reduction in parasiticscan be achieved by disposing power stage 100 as close as possible toload 110 to shorten the path therebetween. For example, power stage 100can be integrated with load 110 in order to reduce the parasitics andincrease the switching speed with consequent reduction in the size ofpassives and increase in efficiency.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1-29. (canceled)
 30. A power management device comprising: a monolithicsemiconductor die having a first III-nitride power semiconductor deviceand a second III-nitride power semiconductor device coupled to saidfirst III-nitride power semiconductor device in a half-bridgeconfiguration; said half-bridge configuration including a first driverhalf-bridge arrangement coupled to said first III-nitride powersemiconductor device, and a second driver half-bridge arrangementcoupled to said second III-nitride power semiconductor device.
 31. Thepower management device of claim 30, wherein said first and seconddriver half-bridge arrangements each includes a pair of enhancement modeIII-nitride switches.
 32. The power management device of claim 30,wherein said first and second driver half-bridge arrangements eachincludes a pair of depletion mode III-nitride switches.
 33. The powermanagement device of claim 30, wherein said first driver half-bridge iscoupled to a level shift circuit that includes a level shift capacitor,wherein said capacitor is formed on a surface of said monolithicsemiconductor die.
 34. The power management device of claim 30, whereinan output node of said half-bridge configuration is coupled to a loadstage that includes a driver control circuitry that generates signalsfor an operation of said first and second driver half-bridgearrangements.
 35. The power management device of claim 34, wherein saiddriver stage control circuitry generates pulse width modulation signals.36. The power management device of claim 34, wherein said signals aregenerated when an output voltage of said power stage falls outside of apre-set range.
 37. The power management device of claim 34, wherein saidsignals are generated due to a load-specific condition.
 38. The powermanagement device of claim 37, wherein said load-specific conditionincludes an instantaneous temperature of said load.
 39. The powermanagement device of claim 37, wherein said load-specific conditionincludes a speed of said load.
 40. The power management device of claim30, further comprising a load stage, wherein said load stage and saidmonolithic semiconductor die are integrated.
 41. The power managementdevice of claim 40, wherein said load stage includes a microprocessor.42. The power management device of claim 40, wherein said load stageincludes a memory device.